TC11钛合金搅拌摩擦焊接头微观组织和力学性能

Microstructural characteristics and mechanical properties of TC11 titanium alloy friction stir welds

摘要:

本文在不同转速下开展了TC11钛合金搅拌摩擦焊试验，分析了接头的微观组织和力学性能，建立了焊接工艺、接头组织与性能之间的内在联系。接头SZ为完全的β转变组织，其细小晶界α相和晶内片层状α+β相以及针状α′相的双重强化作用，致使SZ硬度最高。HAZ和TMAZ均由残余初始α相和β转变组织组成，但后者具有一定的流变特征，且距SZ越近，转变组织占比越大，强化效果越明显。随着转速的上升，SZ中晶界α相和晶内片层状α+β相的尺寸增加，晶内针状α′相的含量降低，这引起了其硬度的降低。与硬度规律相同，各转速下接头拉伸均断裂在BM，且各转速下SZ抗拉强度明显高于BM，并随转速上升而下降。此外，SZ中细小的晶界α相和晶内片层状α+β相，也导致各转速下SZ延伸率高于BM，使其展现出良好的塑性，且随着转速上升，因晶界α相和晶内片层状α+β相尺寸增加，SZ延伸率有所降低。

Abstract:

Friction stir welding of TC11 titanium alloy was carried out under different rotational speeds, the microstructures and mechanical properties of the welded joints were analyzed, and the relationships among processing parameters, microstructures and properties of the joints were established. The SZ produced the fully β transformed microstructure, which contained grain boundary α phase, intragranular lamellar α+β phases and acicular α′ phase. The double strengthening was caused by the fine α phase and α+β phases as well as the presence of α′ phase, which led to the highest hardness value in the SZ. The retained original α phase and β transformed microstructure were found in the HAZ and TMAZ, while the TMAZ showed the streamlined deformation characteristics. The proportion of β transformed microstructure in these zones was higher when closer to the SZ, and thus the strengthening effect was enhanced. The size of α phase and α+β phases increased and the content of α′ phase decreased with the rotational speed ascending, which resulted in the reduction of hardness value in the SZ. Similar to the law reflected from the hardness test, all the joints fractured in BM after tensile test, the tensile strengths of the SZs under different rotational speeds were significantly higher than BM, and they decreased with the ascent of rotational speed. Besides, the fine α phase and α+β phases caused the higher elongations of SZs compared with the BM, meaning that the SZ had the good plasticity. With the rotational speed ascending, the elongations of SZs decreased owing to the increase of the size of α phase and α+β phases.